1. Field of the Invention
The present invention relates to dielectric resonator devices, dielectric duplexers, and communication apparatus incorporating the same, which are used in mobile communication equipment such as cellular phones.
2. Description of the Related Art
Conventionally, as shown in FIG. 13, a dielectric filter formed by coupling a plurality of individual dielectric coaxial resonators has the following structure. A plurality of dielectric coaxial resonators 1a to 1h are mounted on the upper surface of a substrate 2, and a metal cover 3 is attached to the substrate 2 to cover the substrate and the plurality of dielectric coaxial resonators 1a to 1h. The metal cover 3 is electrically connected to grounding electrodes 4 on the substrate 2. In this figure, the metal cover 3 is shown in phantom.
However, in order to miniaturize the mobile communication equipment, by making the dielectric filter having the above structure smaller, it is necessary to reduce the dimensions of the metal cover. A device which can solve the problem, as shown in Japanese Unexamined Patent Application Publication No. 7-235805, is a resonator device in which the upper surfaces of dielectric coaxial resonators are exposed while the coupling parts thereof are covered by a metal cover.
Nevertheless, the structure in which substantially only the coupling parts of the dielectric coaxial resonators are covered by the metal cover causes a problem. There are some parts in which the paths of ground currents flowing from outer conductors of the dielectric coaxial resonators to the grounding electrodes on the substrate tend to be long. Therefore, unless the metal cover is electrically connected very securely to the outer conductors of the dielectric coaxial resonators, the filter characteristics of the device can be deteriorated.
The present invention is able to address these problems by providing a dielectric resonator device, a dielectric duplexer, and a communication apparatus incorporating the same, which can be miniaturized while preventing the deterioration of filter characteristics caused by the reduction in the size of the metal cover.
According to a first aspect of the present invention, there is provided a dielectric resonator device including a plurality of dielectric coaxial resonators having outer conductors and inner conductors, a substrate having the plurality of dielectric coaxial resonators disposed thereon, and a metal cover connected to grounding electrodes on the substrate. In this dielectric resonator device, one dielectric coaxial resonator of the plurality of dielectric coaxial resonators is separated from the adjacent dielectric coaxial resonator by a gap, and a protruding part of the metal cover electrically connects the outer conductors of the adjacent dielectric coaxial resonators to each other in the gap.
With this arrangement, it is not necessary for the metal member to cover the upper surfaces of the plurality of dielectric coaxial resonators. Further, the protruding part provides a short path via the metal cover, for conducting ground currents from one or both of the side surfaces of the pair of adjacent dielectric coaxial resonators, to the closest one of the grounding electrodes on the substrate.
In addition, the metal member may substantially enclose (sufficiently to avoid substantial electromagnetic radiation) at least one of an area close to open-circuited faces of the dielectric coaxial resonators and an area where terminals electrically connected to the inner conductors of the dielectric coaxial resonators are led out.
The protruding part of the metal member may be bonded to the outer conductors of the dielectric coaxial resonators by a conductive bonding agent in the gap.
According to a further aspect of the invention, the protruding part of the metal member may be made of an elastic material.
Furthermore, the metal cover may be formed of sheet metal, and the protruding part of the metal cover may be partially bent. With this arrangement, the protruding part of the metal cover may be made more rigid, and also, the surface area of the regions where the protruding part of the metal cover is bonded to the outer conductors of the dielectric coaxial resonators may be increased.
Furthermore, the protruding part of the metal cover may be ribbed. This increases the rigidity of the protruding part of the metal cover and can also improve bonding reliability. Or, alternatively, a bonding hole may be punched in the protruding part of the metal cover. With this arrangement, as in the case of ribbing, bonding reliability can be improved.
According to a second aspect of the invention, there is provided a dielectric duplexer including the dielectric resonator device described above, a transmission filter and a reception filter each being formed by a respective dielectric resonator device. In this dielectric duplexer, the dielectric coaxial resonators of the transmission filter are separated from the adjacent dielectric coaxial resonators of the reception filter by a gap.
According to a third aspect of the present invention, there is provided a communication apparatus including one of the dielectric resonator device and the dielectric duplexer described above.
Other features and advantages of the present invention will become apparent from the following description of embodiments of the invention which refers to the accompanying drawings.